It is known, for example from U.S. Pat. No. 5,387,439, to manufacture porcelain enamel coatings on steel substrates. The '439 patent addresses a known problem of such coatings: they generally have poor impact strength. Thus, when tools, hardware, debris, or other material forcefully contacts the coating, or the article is subject to rough handling, the coating may be damaged. If a damaged coating encounters a harsh chemical environment such as is present in a chemical manufacturing process, the underlying steel substrate could be etched, and the process would be contaminated by the etched steel. Moreover, the steel substrate ultimately would fail, and the chemical process would no longer be contained or protected from the ambient conditions outside of the steel. The '439 patent discloses coatings having improved impact strength due to the incorporation of inorganic fibrous material into the coating.
Nonetheless, porcelain enamel coatings are still vulnerable to chipping, cracking, and other mechanical damage. The '439 patent teaches that a damaged coating on a process vessel can be corrected with a complete reglassing of the vessel (col. 2, II. 38-41), or by the use of a tantalum (metal and/or oxide) plug (col. 8, II. 14-19). As can be appreciated, reglassing of the entire vessel represents an enormous expense in both repair effort and process downtime, at least because the vessel must be disassembled from the process, typically transported to a repair site that includes a large oven or kiln, reglassed, transported back, and re-assembled into the process. Also, a tantalum patch, usually affixed over the damage site with an epoxy, may alter the chemistry of the process environment. Any repair to glass-lined equipment employing material other than glass is considered temporary.
Other instances of enamel on steel or other metals figure prominently in the economy. So-called white goods, such as washers, dryers, dishwashers, stove tops, ovens, water heaters, and refrigerators, and shower stalls, sinks, and bathtubs also employ sometimes delicate enamel coatings. Each year, manufacturers, distributors, and retailers of such goods must accept a certain loss ratio, because white goods slightly damaged prior to the point of sale are rejected by the consumer. Easy repair of cosmetic damage to such goods would be highly desirable.
Therefore, methods for repairing damage to a porcelain enamel coating resulting in a chemically-resistant coating are desired. Also, methods for repairing such damage that do not require a complete reglassing are also desired. Methods that can be performed in situ or with minimal disassembly are also desired. Furthermore, methods for easily preparing a chemically-resistant coating in the first place are also sought. Methods for repairing a chemically-resistant coating matching the thickness of the existing coating and/or its color are also sought. Articles having a chemically-resistant coating, such as a chemically-resistant coating that is easily repaired, are also desired. The various embodiments of the present invention may meet one or more of those desires, thereby solving the underlying technical problems with current coating manufacturing and repair technology.